Solvent/polymer solutions as suspension vehicles

ABSTRACT

A nonaqueous, single-phase vehicle that is capable of suspending an active agent. The nonaqueous, single-phase vehicle includes at least one solvent and at least one polymer and is formulated to exhibit phase separation upon contact with an aqueous environment. The at least one solvent may be selected from the group consisting of benzyl benzoate, decanol, ethyl hexyl lactate, and mixtures thereof and the at least one polymer may be selected from the group consisting of a polyester, pyrrolidone, ester of an unsaturated alcohol, ether of an unsaturated alcohol, polyoxyethylenepolyoxypropylene block copolymer, and mixtures thereof. In one embodiment, the at least one solvent is benzyl benzoate and the at least one polymer is polyvinylpyrrolidone. A stable, nonaqueous suspension formulation that includes the nonaqueous, single-phase vehicle and an active agent, and a method of forming the same, are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/650,225, filed Feb. 3, 2005.

FIELD OF THE INVENTION

The present invention relates to a suspension vehicle capable ofuniformly dispersing an active agent and delivering the active agent ata low flow rate. More specifically, the present invention relates to asuspension vehicle that includes a solvent and a polymer and isformulated to exhibit phase separation upon contact with an aqueousenvironment.

BACKGROUND OF THE INVENTION

There is considerable interest in delivering small molecules orbiomolecular substances, such as peptides, polypeptides, proteins,lipoproteins, nucleic acid, hormones, viruses, or antibodies, usingimplantable drug delivery devices, such as osmotic, mechanical, orelectromechanical devices. Implantable drug delivery devices provideimproved patient compliance because the devices are not easily tamperedwith by a patient and are designed to provide therapeutic doses of thebiomolecular substance over extended periods of time, such as weeks,months, or even years. Use of the implantable drug delivery device alsoprovides reduced irritation at the site of the implantation compared todaily or multiple injections, fewer occupational hazards for thepatients and practitioners, and reduced waste disposal hazards.Implantable drug delivery devices that are capable of delivering adesired dose of a beneficial agent over extended periods of time areknown in the art.

However, delivering the biomolecular substance with the implantable drugdelivery device is problematic. While the biomolecular substance isactive in an aqueous environment, it is only marginally stable in anaqueous environment under ambient conditions. Therefore, a formulationof the biomolecular substance typically requires refrigeration,otherwise it begins to degrade. The biomolecular substance degrades byone or more mechanisms including deamidation, oxidation, hydrolysis,disulfide interchange, or racemization. Significantly, water is areactant in many of the degradation pathways. In addition, water acts asa plasticizer and facilitates the unfolding and irreversible aggregationof the biomolecular substance. To overcome the stability problems withaqueous formulations of the biomolecular substance, dry powderformulations of the biomolecular substance have been created using knownparticle formation processes, such as lyophilization, spray-drying,freeze-drying, or dessication of the biomolecular substance. While dryformulations of the biomolecular substances are stable, many deliverymethods require flowable forms of the biomolecular substance. Forinstance, flowable forms are needed for parenteral injections andimplantable drug delivery devices.

To form a flowable formulation, a dry, powdered biomolecular substanceis typically suspended in a nonaqueous, viscous vehicle. Thebiomolecular substance must be contained within a formulation thatmaintains the stability of the biomolecular substance at an elevatedtemperature (i.e., 37° C. and above) over the operational life of theimplantable drug delivery device. The biomolecular substance must alsobe formulated to allow delivery of the biomolecular substance into adesired environment of operation over an extended period of time. Thebiomolecular substance must also be formulated to allow delivery at alow flow rate (i.e., less than or equal to approximately 100 μl/day).

U.S. Pat. No. 6,468,961 to Brodbeck et al. and United States PatentApplication Nos. 2004/0024069 and 2004/0151753, both to Chen et al.,disclose a depot composition that includes a viscous gel formed from apolymer and a solvent. The polymer is a polylactide, polyglycolide,caprolactone-based polymer, polycaprolactone, polyanhydride, polyamine,polyurethane, polyesteramide, polyorthoester, polydioxanone, polyacetal,polyketal, polycarbonate, polyorthocarbonate, polyphosphazene,succinate, poly(malic acid), poly(amino acid), polyvinylpyrrolidone(PVP), polyethylene glycol, polyhydroxycellulose,hydroxymethylcellulose, polyphosphoester, polyester, polyoxaester,polybutylene terephthalate, polysaccharide, chitin, chitosan, hyaluronicacid, or copolymer, terpolymer, or mixtures thereof. The solventincludes aromatic alcohols; esters of aromatic acids, such as loweralkyl or aralkyl esters of aryl acids; aromatic ketones, such as aryl,aralkyl, or lower alkyl ketones; and mixtures thereof.

United States Patent Application No. 2003/0108609 to Berry et aldiscloses a stable, nonaqueous single phase viscous vehicle thatincludes at least two of a polymer, a solvent, and a surfactant. Thevehicle suspends a beneficial agent, which is deliverable at a low flowrate and at body temperature from an implantable drug delivery device.The solvent includes carboxylic acid esters, polyhydric alcohols,polymers of polyhydric alcohols, fatty acids, oils, lauryl alcohol, oresters of polyhydric alcohols. The polymer includes polyesters,pyrrolidones, esters or ethers of unsaturated alcohols, orpolyoxyethylenepolyoxypropylene block copolymers. The vehicle is wellsuited to preparing suspensions that include biomolecular beneficialagents and are stable over extended periods of time, even at elevatedtemperatures. However, under certain circumstances, a formulation of thevehicle and the beneficial agent may have the potential to inhibitdelivery of the beneficial agent into the desired environment ofoperation. In particular, when the formulation is exposed to an aqueousliquid, such as a physiological fluid, within a delivery conduit of adevice used to deliver the formulation, the polymer in the vehicle tendsto phase separate from the solvent into the aqueous liquid. As thepolymer partitions into the aqueous liquid, the concentration of thepolymer within the aqueous liquid may increase to such an extent that ahighly viscous polymer gel is formed within the delivery conduit, whichresults in a partial or complete occlusion of the delivery conduit andinterferes with the desired operation of the delivery device. Thepotential for such occlusions increases where the geometry of thedelivery conduit is such that aqueous liquid interfaces with the drugformulation in a confined area over a relatively long period of time(e.g., hours or days).

It would be an improvement in the art to provide a vehicle thatfacilitates delivery of a formulation of a small molecule orbiomolecular substance from a depot composition or an implanted drugdelivery device. Ideally, the vehicle is formulated to deliver thetherapeutic agent at a controlled rate without blocking or occluding thedrug delivery device and/or to maintain the stability of thebiomolecular substance over an extended period of time.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a nonaqueous, single-phase vehicle thatis capable of suspending an active agent. The nonaqueous, single-phasevehicle includes at least one solvent and at least one polymer, and isformulated to exhibit phase separation upon contact with an aqueousenvironment. The at least one solvent may be immiscible with water andthe at least one polymer may be soluble in the at least one solvent. Theat least one solvent may be selected from the group consisting of benzylbenzoate, decanol, ethyl hexyl lactate, and mixtures thereof. The atleast one polymer may be selected from the group consisting of apolyester, pyrrolidone, ester of an unsaturated alcohol, ether of anunsaturated alcohol, polyoxyethylenepolyoxypropylene block copolymer,and mixtures thereof. In one embodiment, the at least one solvent isbenzyl benzoate and the at least one polymer is polyvinylpyrrolidone(PVP).

The present invention also relates to a stable, nonaqueous suspensionformulation that includes an active agent and a nonaqueous, single-phasevehicle. The nonaqueous, single-phase vehicle includes at least onesolvent and at least one polymer and is formulated to exhibit phaseseparation upon contact with an aqueous environment. The at least onesolvent and the at least one polymer may be one of the materialsdescribed above. The active agent may be selected from the groupconsisting of baclofen, glial-cell line-derived neurotrophic factor, aneurotrophic factor, conatonkin G, Ziconotide, clonidine, axokine, anantisense oligonucleotide, adrenocorticotropic hormone, angiotensin I,angiotensin II, atrial natriuretic peptide, B-natriuretic peptide,bombesin, bradykinin, calcitonin, cerebellin, dynorphin N, alphaendorphin, beta endorphin, endothelin, enkephalin, epidermal growthfactor, fertirelin, follicular gonadotropin releasing peptide, galanin,glucagon, glucagon-like peptide-1, gonadorelin, gonadotropin, goserelin,growth hormone releasing peptide, histrelin, human growth hormone,insulin, an alpha-, beta-, or omega-interferon, Nesiritide, leuprolide,luteinizing hormone-releasing hormone, motilin, nafarerlin, neurotensin,oxytocin, relaxin, somatostatin, substance P, tumor necrosis factor,triptorelin, vasopressin, growth hormone, nerve growth factor, a bloodclotting factor, and a ribozyme. In one embodiment, the at least onesolvent is benzyl benzoate, the at least one polymer ispolyvinylpyrrolidone, and the active agent is omega-interferon(omega-INF). The active agent may also be selected from small moleculessuch as, for example, ocaperidone, risperidone, and paliperidone.

The present invention also relates to a method of preparing a stable,nonaqueous suspension formulation. The method includes providing anonaqueous, single-phase vehicle that includes at least one polymer andat least one solvent. The nonaqueous, single-phase vehicle exhibitsphase separation upon contact with an aqueous environment. An activeagent is provided, wherein the active agent is substantially insolublein the nonaqueous, single-phase vehicle. The active agent and thenonaqueous, single-phase vehicle are mixed to form a stable, nonaqueoussuspension formulation. The at least one solvent, the at least onepolymer, and the active agent may be one of the materials describedabove.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention may be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a graph illustrating the viscosity of a suspension vehiclethat includes benzyl benzoate and PVP as a function of the weightpercentage of PVP;

FIG. 2 illustrates the percentage of total omega-INF that appears as theunaltered omega-IFN main peak in suspension vehicles that include (i)benzyl benzoate and PVP and (ii) benzyl benzoate, benzyl alcohol, andPVP at 40° C. as a function of time;

FIG. 3 illustrates the percentage of the total omega-IFN present in thesuspension vehicle that is in the deamidated state in suspensionvehicles that include (i) benzyl benzoate and PVP and (ii) benzylbenzoate, benzyl alcohol, and PVP at 40° C. as a function of time;

FIG. 4 illustrates the total percentage of the total omega-IFN presentin the suspension vehicle that is in the oxidated state in suspensionvehicles that include (i) benzyl-benzoate and PVP and (ii) benzylbenzoate, benzyl alcohol, and PVP at 40° C. as a function of time;

FIG. 5 illustrates the percentage of dimerization of omega-INF insuspension vehicles that include (i) benzyl benzoate and PVP and (ii)benzyl benzoate, benzyl alcohol, and PVP at 40° C. as a function oftime;

FIGS. 6 and 7 illustrate the average total omega-INF released and theaverage percentage of soluble omega-INF released, respectively, from asuspension vehicle that includes benzyl benzoate and PVP;

FIG. 8 illustrates the stability (dimerization, oxidation, deamidation,and related proteins) of omega-INF in a suspension vehicle that includesbenzyl benzoate and PVP;

FIG. 9 is a graph illustrating the in vivo release of omega-INF in rats;and

FIG. 10 shows the serum level distributions of omega-INF nine days afterimplantation.

DETAILED DESCRIPTION OF THE INVENTION

A suspension formulation having a suspension vehicle and an active agentis disclosed. The suspension vehicle is formulated to exhibit phaseseparation upon contact with an aqueous environment. As used herein, thephrase “phase separation” refers to the formation of multiple phases(e.g., liquid or gel phases) in the suspension vehicle, such as when thesuspension vehicle contacts the aqueous environment. In specificembodiments of the invention, the suspension vehicle is formulated toexhibit phase separation upon contact with an aqueous environment havingless than approximately 10% water. The suspension vehicle is asingle-phase vehicle in which the active agent is dispersed. As usedherein, the phrase “single-phase” refers to a solid, semisolid, orliquid homogeneous system that is physically and chemically uniformthroughout, as determined by differential scanning calorimetry (DSC). Asused herein, the term “dispersed” refers to dissolving, dispersing,suspending, or otherwise distributing the active agent in the suspensionvehicle. The suspension vehicle is formulated to provide sustaineddelivery of the active agent to a patient by delivering the active agentat a low flow rate over an extended period of time. As used herein, theterm “patient” refers to a human or another mammal to which thesuspension formulation is administered.

The suspension vehicle provides a stable environment in which the activeagent is dispersed. The suspension vehicle includes at least one polymerand at least one solvent, forming a solution of sufficient viscosity touniformly suspend particles of the active agent. The viscosity of thesuspension vehicle may prevent the active agent from settling duringstorage and use of the suspension formulation in, for example, animplantable, drug delivery device. The suspension vehicle isbiodegradable in that the suspension vehicle disintegrates or breaksdown over a period of time in response to a biological environment. Thedisintegration of the suspension vehicle may occur by one or morephysical or chemical degradative processes, such as by enzymatic action,oxidation, reduction, hydrolysis (e.g., proteolysis), displacement(e.g., ion exchange), or dissolution by solubilization, emulsion ormicelle formation. After the suspension vehicle disintegrates,components of the suspension vehicle are absorbed or otherwisedissipated by the body and surrounding tissue of the patient.

The solvent in which the polymer is dissolved may affect characteristicsof the suspension formulation, such as the behavior of the active agentduring storage and, where applicable, use of the implantable, drugdelivery device. The solvent may be selected in combination with thepolymer so that the resulting suspension vehicle exhibits phaseseparation upon contact with the aqueous environment. Optionally, thesolvent may be selected in combination with the polymer so that theresulting suspension vehicle exhibits phase separation upon contact withthe aqueous environment having less than approximately 10% water. Thesolvent may be a pharmaceutically acceptable solvent that is notmiscible with water. The solvent may also be selected so that thepolymer is soluble in the solvent at high concentrations, such as at apolymer concentration of greater than approximately 30%. However, theactive agent may be substantially insoluble in the solvent. The solventmay include, but is not limited to, lauryl alcohol, benzyl benzoate,benzyl alcohol, lauryl lactate, CERAPHYL® 31, decanol (also called decylalcohol), ethyl hexyl lactate, and long chain (C8 to C24) aliphaticalcohols, esters, or mixtures thereof. The solvent used in thesuspension vehicle may be “dry,” in that it has a low moisture content.In one embodiment, the solvent is benzyl benzoate, which has asolubility in water of less than approximately 0.01%. Using benzylbenzoate as the solvent can be advantageous because benzyl benzoate isused as an excipient in injectable products, such as DELESTROGEN® andFASLODEX®. As such, the risk of the patient suffering adverse reactionsto benzyl benzoate is reduced and the cost to demonstrate safety of thebenzyl benzoate is decreased.

The polymer may include, but is not limited to, a polyester,pyrrolidone, ester or ether of an unsaturated alcohol,polyoxyethylenepolyoxypropylene block copolymer, or mixtures thereof.The polyester may be polylactic acid or polylacticpolyglycolic acid. Thepyrrolidone may be PVP having a molecular weight ranging fromapproximately 2,000 to approximately 1,000,000. The ester or ether ofthe unsaturated alcohol may be vinyl acetate. In one embodiment, thepolymer is PVP. The polymer used in the suspension vehicle may includeone or more different polymers or may include different grades of asingle polymer. The polymer used in the suspension vehicle may also bedry or have a low moisture content.

The polymer and the solvent may each be present in the suspensionvehicle in an amount sufficient to provide the desired performance ofthe suspension vehicle. The polymer may be present in the suspensionvehicle from approximately 10% to approximately 90% and the solvent maybe present from approximately 10% to approximately 90%. The percentagesof the polymer and the solvent are provided herein in terms of wt/wtratios. For instance, the suspension vehicle may include fromapproximately 25% to approximately 75% of the polymer and fromapproximately 25% to approximately 75% of the solvent. In oneembodiment, the suspension vehicle includes from approximately 40% toapproximately 60% of the polymer and from approximately 40% toapproximately 60% of the solvent.

The suspension vehicle may exhibit Newtonian behavior. The suspensionvehicle is formulated to provide a viscosity that maintains the uniformdispersion of the active agent for a predetermined period of time, whichfacilitates creation of a suspension formulation that is tailored toprovide controlled delivery of the active agent at a desired rate. Theviscosity of the suspension vehicle may vary depending on the desiredapplication, the size and type of the active agent, and the loading ofthe active agent in the suspension vehicle. The viscosity of thesuspension vehicle may be varied by altering the type or relative amountof the solvent or polymer used. The suspension vehicle may have aviscosity ranging from approximately 100 poise to approximately1,000,000 poise, such as from approximately 1,000 poise to approximately100,000 poise. The viscosity is measured at 37° C., at a shear rate of10⁻⁴/sec, using a parallel plate rheometer. In one embodiment, theviscosity of the suspension vehicle ranges from approximately 5,000poise to approximately 50,000 poise. While the suspension vehicleexhibits phase separation when contacted with the aqueous environment,the suspension vehicle may exhibit substantially no phase separation asa function of temperature. For instance, at a temperature ranging fromapproximately 0° C. to approximately 70° C. and upon temperaturecycling, such as cycling from 4° C. to 37° C. to 4° C., the suspensionvehicle may exhibit no phase separation. In particular embodiments ofthe invention, the suspension vehicle exhibits phase separation whencontacted with the aqueous environment having less than approximately10% water.

The suspension vehicle may be prepared by combining the polymer and thesolvent under dry conditions, such as in a dry box. The polymer andsolvent may be combined at an elevated temperature, such as fromapproximately 40° C. to approximately 70° C., and allowed to liquefy andform the single phase. The ingredients may be blended under vacuum toremove air bubbles produced from the dry ingredients. The ingredientsmay be combined using a conventional mixer, such as a dual helix bladeor similar mixer, set at a speed of approximately 40 rpm. However,higher speeds may also be used to mix the ingredients. Once a liquidsolution of the ingredients is achieved, the suspension vehicle may becooled to room temperature. DSC may be used to verify that thesuspension vehicle is a single phase.

The active agent may be added to the suspension vehicle to form thesuspension formulation. The active agent may be a biomolecular substancethat has biological activity or is capable of being used to treat adisease or other pathological condition. The active agent may include,but is not limited to, a peptide, polypeptide, protein, amino acids,nucleotides, a polymer of an amino acid residue(s) or a nucleotideresidue(s), hormone, virus, antibody, or mixtures thereof. Thebiomolecular substance may also be a conjugated protein, such as alipoprotein or post translationally modified form thereof, such as aglycosylated protein or a protein substance having D-amino acids,modified, derivatized, or non-naturally occurring amino acids in the D-or L-configuration, and/or peptomimetic units. The biomolecularsubstance may be naturally derived, synthetically produced, orrecombinantly produced. The active agent may also be an organiccompound, such as a drug, medicine, vitamin, nutrient, or foodsupplement. The active agent may be used in a solid state, such as apowder, crystalline, or amorphous state. As such, the active agent maybe dry or may have a low moisture content. The active agent may bestable at ambient and physiological temperatures in the solid state. Theactive agent may also be used in the form of a pharmaceuticallyacceptable salt, such as a salt of an inorganic acid, an organic acid,an inorganic base, or an organic base. As previously mentioned, theactive agent may have little or no solubility in the suspension vehicle.The active agent can be selected to provide a therapeutic or beneficialeffect when administered to the patient. For the sake of example only,the active agent may be used as a treatment for Hepatitis C, heartdisease, diabetes, cancer, bone disease, autoimmune disease,gastrointestinal diseases, respiratory disease, kidney disease, liverdisease, circulatory diseases, blood disorders, hormonal disorders,genetic disorders, metabolic disorders, thyroid disease, or centralnervous system disorders.

Examples of active agents that may be utilized in the suspensionformulation include, but are not limited to, baclofen, glial-cellline-derived neurotrophic factor (GDNF), neurotrophic factors,conatonkin G, Ziconotide, clonidine, axokine, antisenseoligonucleotides, adrenocorticotropic hormone, angiotensin I and II,atrial natriuretic peptide, B-natriuretic peptide (BNP), bombesin,bradykinin, calcitonin, cerebellin, dynorphin N, alpha and betaendorphin, endothelin, enkephalin, epidermal growth factor, fertirelin,follicular gonadotropin releasing peptide, galanin, glucagon,glucagon-like peptide (GLP)-1, gonadorelin, gonadotropin, goserelin,growth hormone releasing peptide, histrelin, human growth hormone,insulin, interferons (INF), such as omega-INF, leuprolide, Nesiritide,luteinizing hormone-releasing hormone (LHRH), motilin, nafarerlin,neurotensin, oxytocin, relaxin, somatostatin, substance P, tumornecrosis factor, triptorelin, vasopressin, growth hormone, nerve growthfactor, blood clotting factors, and ribozymes. The active agent may alsobe selected from small molecules such as, for example, ocaperidone,risperidone, and paliperidone. Analogs, derivatives, antagonists,agonists, and pharmaceutically acceptable salts of the active agentsmentioned above may also be used. In one embodiment, the active agent isomega-INF.

The amount of the active agent present in the suspension formulation mayvary depending on the potency of the active agent, the disease orcondition to be treated, the solubility of the active agent, the dose tobe administered, the duration of administration, and the desired releaserate. The active agent may be present in the suspension formulation inan amount that ranges from approximately 0.1% (w/w) to approximately 50%(w/w). The suspension formulation may include from approxirnately 50%(w/w) to 99.9% (w/w) of the suspension vehicle. In one embodiment, theparticle containing the active agent is present in the suspensionformulation at approximately 3-12% 10% (w/w).

The active agent used in the suspension formulation may be provided as astabilized, dry powder that is produced by spray-drying, freeze-drying,a supercritical fluid process, dessication, granulation, grinding,milling, precipitation, homogenization, or a coating process, as knownin the art. To provide the active agent as the dry powder, the activeagent may be formulated with one or more adjuvants, excipients,stabilizers, bulking agents, preservatives, or coating agents, as knownin the art. For instance, the active agent may be formulated with atleast one of citrate, histidine, succinate, methionine, sucrose, anddextran. In one embodiment, the suspension formulation includesomega-INF:sucrose:methionine:citrate at a ratio of 1:2:1:2.15.

The suspension formulation may be used in the implantable, drug deliverydevice to provide sustained delivery of the active agent over anextended period of time, such as over weeks, months, or up toapproximately one year. The suspension formulation may be prepared bydispersing the active agent in the suspension vehicle. The suspensionvehicle may be heated and the active agent added to the suspensionvehicle under dry conditions. The ingredients may be mixed under vacuumat an elevated temperature, such as from approximately 40° C. toapproximately 70° C. The ingredients may be mixed at a sufficient speed,such as from approximately 40 rpm to approximately 120 rpm, and for asufficient amount of time, such as approximately 15 minutes, to achievea uniform dispersion of the active agent in the suspension vehicle. Themixer may be a dual helix blade or other suitable mixer. The resultingmixture may be removed from the mixer, sealed in a dry container toprevent water from contaminating the suspension formulation, and allowedto cool to room temperature before loading into the implantable, drugdelivery device. The suspension formulation may be loaded into theimplantable, drug delivery device by conventional techniques. Theresulting suspension formulation may be stable when stored at elevatedtemperatures or for an extended period of time.

The suspension formulation may also be used in the form of depotinjections to provide sustained delivery of biologically activemacromolecules and small molecule compounds. The suspension formulationmay be designed to deliver agents for periods of days to months.Alternatively, the suspension formulation may be loaded into animplantable, drug delivery device, which may be capable of deliveringthe active agent at a desired flow rate over a desired period of time.For example, the suspension formulation may be delivered by anosmotically, mechanically, electromechanically, or chemically drivendrug delivery devices. The flow rate at which the active agent isdelivered may be less than approximately 100 μl/day, such as fromapproximately 0.5 μl/day to approximately 5 μl/day. The active agent maybe delivered over a period ranging from more than approximately one weekto approximately one year or more. The implantable, drug delivery devicemay include a reservoir having at least one orifice through which theactive agent is delivered. The suspension formulation may be storedwithin the reservoir. The suspension formulation may also be deliveredfrom a drug delivery device that is not implantable or implanted. In oneembodiment, the implantable, drug delivery device is osmotically driven,such as a DUROS® implant, which is available from ALZA Corp. (MountainView, Calif.). The DUROS® implant may enable continuous delivery of theactive agent for an extended duration, such as for up to approximatelyone year.

Other exemplary implantable, drug delivery devices may includeregulator-type implantable pumps that provide constant flow, adjustableflow, or programmable flow of the active agent, such as those availablefrom Codman & Shurtleff, Inc. (Raynham, Mass.), Medtronic, Inc.(Minneapolis, Minn.), and Tricumed Medinzintechnik GmbH (Germany).

Phase separation of the suspension vehicle may occur when the suspensionvehicle contacts the aqueous environment, forming a second phase that isrich in water and the polymer. The second phase includes substantiallyno solvent. Since the active agent is stable in nonaqueous and diluteaqueous environments, the active agent may remain stably dispersed afterthe phase separation occurs. In contrast, the active agent is not stablein environments that include moderate quantities of water, such as fromapproximately 10% to 25% water.

In a particular embodiment where a drug delivery device is implanted inthe patient, water from surrounding tissues may enter one end of theimplantable, drug delivery device through a semipermeable membrane. Thewater may also cause an osmotic engine in the implantable, drug deliverydevice to swell, displacing a piston and releasing the suspensionformulation from a second end of the implantable, drug delivery deviceand into the patient's body.

Without being bound to any theory, it is believed that the suspensionvehicle is capable of effectively delivering the active agent to thepatient due to the environment that the active agent encounters as theactive agent transitions from the dry suspension formulation to thedilute aqueous environment. If the suspension vehicle is incorporatedinto an implantable, drug delivery device, the suspension vehicle iscapable of effectively delivering the active agent to the patient due tothe environment that the active agent encounters as the active agenttransitions from the dry suspension formulation within the implantable,drug delivery device to the dilute aqueous environment outside of theimplantable drug delivery device.

The following examples serve to explain embodiments of the presentinvention in more detail. These examples are not to be construed asbeing exhaustive or exclusive as to the scope of this invention.

EXAMPLES Example 1 Stability and In Vitro Release of Omega-INF in aBenzyl Benzoate and a Benzyl Benzoate/Benzyl Alcohol Suspension Vehicle

The stability of omega-INF for three months at 40° C. in two suspensionvehicles was determined. One of the suspension vehicles included PVPdissolved in benzyl benzoate. The second suspension vehicle included PVPdissolved in a 90/10 benzyl benzoate/benzyl alcohol mixture. A releaserate study at 37° C. was also performed. The materials used in thestability and release rate studies are shown in Table 1. TABLE 1Materials to be used in the Stability and Release Rate Studies.Spray-dried omega-IFN: sucrose:methionine:citrate (1:2:1) in 25 mMcitrate buffer Benzyl benzoate (BB) Benzyl alcohol (BA)Polyvinylpyrrolidone (PVP) Citrate Buffer Phosphate Buffered Saline(PBS) Piston, fluoroelastomer DUROS ® Osmotic Tablet TecophilicHP-60D-33 Membrane (g2) Blue NB 7443: 155 Titanium Reservoir (g2)Polyethylene Glycol 400 Silicone Fluid, MDM 350 Spiral DiffusionModerator (DM), high density polyethylene (HDPE), 10 mil, 0.43 mm 10 ccOSGE Glass Syringes

To produce the spray-dried omega-INF, omega-INF was combined withsucrose and methionine dissolved in a 25 mM pH 6.0 citrate buffer andthen spray-dried. Spray-drying was conducted and particles collected ina clean, dry air isolator. Particles were tested for purity, proteincontent, moisture content, oxidation, deamidation, degradation,aggregation, and particle size distribution, as known in the art.

Since the solvents are likely to contain peroxide residues, theperoxides were removed from the benzyl benzoate and benzyl alcoholbefore preparing the suspension vehicle. To remove the peroxides,alumina was mixed with each of the benzyl benzoate and benzyl alcoholfor 30 minutes. The solvents were then filtered through a 0.2 μm filterand stored in a sealed vial under nitrogen. The peroxide levels weremeasured for each of the benzyl benzoate and benzyl alcohol, as known inthe art, before using the solvents in the suspension vehicle. Beforeuse, the PVP was treated with a solution of methionine to reduce theperoxide content. The solution was then diafiltered to remove themethionine, and lyophilized to remove water, leaving a cake of the PVP.Peroxide levels in the PVP were measured as known in the art.

The suspension vehicle was prepared in a DIT mixer at 65° C. The waterbath temperature was set to approximately 65° C. and the mixer waspreheated. Appropriate amounts of the benzyl benzoate and/or benzylalcohol were weighed into the mixing bowl. An appropriate amount of thePVP was weighed and transferred into the mixing bowl. The mixing bowlwas mounted and the ingredients stirred to incorporate the PVP into thesolvent. A vacuum (−5 to −10 in Hg) was applied during the mixing. Afterthe PVP was visually incorporated into the solvent, the vacuum wasincreased to −30 in Hg, the bowl temperature adjusted to 60° C., and theingredients were mixed for two hours. The suspension vehicle wasdischarged into a glass jar and degassed in a vacuum oven set at 60° C.and −30 in Hg for approximately 4-6 hours. The solvent/PVP ratio wasselected so that the suspension vehicle had a viscosity of between10,000 poise and 20,000 poise. As shown in FIG. 1, the viscosity of theBB/PVP suspension vehicle is within the desired range.

The suspension formulation including the suspension vehicle and theomega-INF particles was prepared in a dry box under nitrogen. A hotplate was moved into the dry box and preheated to 60° C. Appropriateamounts of the omega-INF and the suspension vehicle were weighed into aglass beaker. Using a stainless steel spatula, the omega-INF particleswere manually incorporated into the suspension vehicle while warming thesuspension vehicle with the hotplate. The suspension formulation wasmixed by hand for 15 minutes. The suspension formulation included 1:2:1omega-INF:sucrose:methionine by weight with 25 mM citrate buffer. Theparticle loading of omega-INF in the suspension was approximately 10%,which is equivalent to a drug loading of approximately 1.7%. This isconsistent with a unit dose of 25 pg/day of the omega-INF.

Using a spatula, the suspension formulation was filled into a 10 mL OSGEsyringe and the syringe plunger inserted to seal the syringe. An ovenwas preheated to 60° C. and the filled syringe was transferred to thevacuum oven while a nitrogen flow was on to purge the vacuum oven ofoxygen. The plunger was removed and a deaeration spring inserted intothe syringe. The formulation was allowed to equilibrate to oventemperature. The spring was rotated at a target of 100 RPM and a vacuumslowly applied until approximately −30 in Hg was attained. The springwas used to mix the suspension formulation for 30 minutes under vacuum.After deaeration, the plunger was inserted into the syringe and excessair was removed. The syringe was sealed in polyfoil and storedrefrigerated (at 2° C.-8° C.).

System samples for the release rate and stability studies were filled onthe benchtop under ambient conditions. To form the systems,subassemblies were produced by lubricating the reservoirs and pistonswith SMF 350. The piston was inserted into the reservoir and −20 μL ofPEG400 was dispensed on the piston. Two osmotic tablets were insertedinto the subassembly and an annealed and dried membrane was insertedinto the reservoir. The subassemblies were annealed for 30 minutes at65° C. A filling needle was attached to the syringe containing thesuspension formulation. The glass syringe was loaded into a Harvardsyringe pump with a heating block surrounding the barrel of the syringeand heated to 65° C. The subassembly was placed on the needle and theimplant reservoir filled to within approximately ¼″ of the end. Aliquotsof the suspension formulation for stability testing were dispensed intoglass vials. The vials were flushed with nitrogen, capped, sealed, andstored at 40° C.

To test the systems, the membrane end was placed into a stopperedVACUTAINER® with 3 mL of PBS (phosphate buffer) and the capillary ordiffusion moderator end of the assembly was placed into a dry vial(primed) or a vial filled with 3 mL of citrate buffer (unprimed). Thesystem was placed into a 37° C. oven or water bath. For primed systems,the diffusion moderator side vial was filled with citrate buffer afterthe suspension formulation was observed to exit from the implants(several days to 1 week). For the primed systems, the buffer vial wasreplaced with a new vial containing fresh buffer one day after fillingthe diffusion moderator side vial. The old vial was submitted forprotein assay. Once per week, the vial was removed from the diffusionmoderator of the system for protein assay determination. A new vial withbuffer was placed onto the system and the implant returned to 37° C. Thesamples for protein assay were stored in a refrigerator at 4° C.

The stability of the omega-INF in the suspension formulation wasmeasured after storage at 40° C. in glass vials flushed with nitrogen.The stability samples were tested in triplicate at t=0, 2, 4, 8, and 12weeks. The samples were analyzed using reversed-phase high pressureliquid chromatography (RP-HPLC) to determine purity with respect tooxidation and deamidation, and using size exclusion chromatography (SEC)to determine purity with respect to aggregation and precipitation. Asshown in FIG. 2, the measured levels of omega-INF did not change overtime in the benzyl benzoate/PVP suspension vehicle. In addition, asshown in FIG. 3, deamidation of the omega-INF was unchanged between 0and 12 weeks. Oxidation of the omega-INF was also unchanged between 0and 8 weeks but increased slightly after 12 weeks, as shown in FIG. 4.Dimerization levels of the omega-INF increased from 0 to 2 weeks but didnot increase from 2 to 12 weeks, as shown in FIG. 5.

A rate at which the suspension vehicles released the omega-IFN into anaqueous medium at 37° C. was determined. The release rate study wasperformed using the systems described above. The spiral diffusionmoderator was formed from HDPE having an internal diameter of 0.43 mmand a path length of 5 cm. The groups and group size in the release ratestudy are shown in Table 2. TABLE 2 Release Rate Experimental Plan.Suspension 191-1 Start-up Conditions BB/PVP Dry start, spiral DM 12 Wetstart, spiral DM 12

The citrate buffer included 50 mM citric acid at pH 2 with 0.2% sodiumazide added as an antibacterial agent. In all systems, the membrane sideof the system is exposed to PBS.

As shown in FIGS. 6 and 7, good in vitro release performance wasobserved with the benzyl benzoate/PVP suspension vehicle when thesuspension vehicle contacted citrate buffer at 37° C. In addition, atday 89, all of the systems had intact membranes. The average totalomega-INF released was also near the target (25 ag/day) through 70 days.

Example 2 In Vivo and In Vitro Testing of Suspension Formulations Usinga Straight Diffusion Moderator

Four suspension formulations were tested under in vivo conditions over90 days in rats to determine stability and in vivo release of theomega-INF. The suspension formulations included omega-INF as the activeagent, PVP or dioleoyl-phosphocholine (DOPC) as the thickening agent,and lauryl alcohol (LA), benzyl benzoate, benzyl alcohol, or Vitamin Eas the solvent. This experiment was designed to concentrate on thesuspension formulations and used a straight polyetheretherketone (PEEK)diff-usion moderator having a 0.25 mm diameter and a 15 mm length tominimize water ingress. During the experiment, efforts were made tominimize the moisture levels to which the suspension formulation wasexposed. The suspension formulations were tested to determine omega-INFrelease in vivo from the DUROS® systems at t=5, 9, and 13 days; failurerates (system integrity) of in vivo systems at 45 days (n=3) and 90 days(n=20) after implantation; stability assessment at 5° C. for 3, 6, and12 months and 40° C. for 1, 2, 3, and 6 months; and in vitro releaserate pumping into the air. The materials used in this experiment areshown in Table 3. TABLE 3 Materials Used in the Studies. MaterialOmega-INF Sucrose Methionine Citrate buffer Povidone 17PF (cleaned)Lauryl Alcohol Benzyl Benzoate Benzyl Alcohol DOPC Vitamin E DUROS ®Implants C-FLEX ® Piston Material Fluoroelastomer Piston DUROS ® OsmoticTablet Tecophilic HP-60D-33 DUROS ® Membrane Titanium Reservoir (Gen 3)with colored band Polyethylene Glycol 400 Silicone Fluid, MDM 350Straight PEEK DM (0.25 × 15 mm)The DUROS® implants used a 150 microliter Gen 3 titanium reservoir witha colored band (drawing no. 28503) fitted with clear TecophilicHP-60D-33 membranes annealed for 7 days at 65° C.

Each of the suspension vehicles was prepared in a 60 g lot. To minimizeresidual moisture levels, lyophilized PVP (Povidone) was used. Themoisture content of the PVP was measured before preparing the suspensionvehicles. The PVP-based suspension vehicles were prepared using aLightnin Overhead Mixer fitted with a spatula blade for the stirringpaddle. The DOPC-based vehicle was prepared on a Keynes mixer. Thesuspension vehicles were visually inspected for particulates beforeproceeding. The suspension vehicles were also inspected for phaseseparation under the microscope at 40° C., 5° C., 0C, and −5° C. Asummary of the compositions of the suspension vehicles is presented inTable 4.

The omega-INF was prepared as described in Example 1, except that thefinal target composition of the omega-INF particles was 1:2:1:2.15(omega-INF:sucrose:methionine:citrate). Each suspension formulation hada target particle loading of approximately 10% (w/w). The incorporationof the omega-INF particles into the suspension vehicle was conducted ina Scott Turbon Mixer in 25 g lots. Following deaeration, the sampleswere filled in 10 mL syringes and sealed in polyethylene and polyfoilpouches. Samples of the suspension formulations were stored refrigerateduntil filling. TABLE 4 Target Compositions of Suspension FormulationsSuspension Vehicle Composition Drug Particle Composition Content ContentSucrose Methionine Citrate ω-INF Formulation Solvent (% w/w) Agent (%w/w) (% w/w) (% w/w) (% w/w) (% w/w) PDP7-200-1 LA 40.5 PVP 49.5 3.3%1.6% 3.5% 1.6% PDP7-200-2 BB 44.1 45.9 PDP7-200-3 BA 35.1 54.9PDP7-200-4 Vit. E 43.2 DOPC 46.8

The subassemblies were prepared as described in Example 1. Thesubassemblies and diffusion moderators for the systems were sterilizedby gamma irradiation. The subassemblies were passed into and out of thedry box without subjecting the systems to purging to avoid the implantsexperiencing a reduced pressure environment. The subassemblies werefilled with the suspension formulation in the dry box using a heatedsyringe pump. The systems were then placed into labeled vials with theirmembrane side down and stoppered, but not crimped. The systems wereremoved from the dry box and fitted with a straight PEEK diff-usionmoderator with channel dimensions of 0.25 mm×15 mm. The vials wereopened just prior to diffusion moderator insertion. The vials were thenrestoppered and brought back into the dry box in batches to ensure thatthe exposure time outside the dry box did not exceed 30 minutes. Eachsystem was equilibrated unstoppered in the dry box for 30 minutes beforebeing re-stoppered and crimped. The vials were then taken out of the drybox and the air bubbles in each system were assessed using X-Rays. Tensystems and diffusion moderators were weighed pre- and post-filling, aswell as three systems filled with silicone medical fluid. This data wasused to assess the amount of air in each system. Systems were built forin vivo studies and stability. Three systems were exposed to the ambientenvironment for 30 minutes to quantify moisture uptake.

Each of the systems was characterized as indicated in Table 5. Thehomogeneity of each of the system samples was tested by monitoring thecontent of the omega-INF at the beginning, middle, and end of the batchin replicates of three. This data was also used as the t=0 stabilitydata point. TABLE 5 Characterization Testing of Systems. Samplingquantity and format Tests per suspension formulation In Vivo 29 ImplantsProtein Content Assay 3 × 0.2 g (beginning) in vials (t = 0 homogeneity)(homogeneity + 3 × 0.2 g (middle) in vials (t = 0 homogeneity)stability) 3 × 0.2 g (end) in vials (t = 0 homogeneity) 21 Implants(stability n = 3, 7 conditions) Bioburden 3 Implants Endotoxin 1 ImplantX-ray All Viscosity 1 ml Density 10 systems (these systems can be alsoused for stability) Moisture (30 min 3 systems (no DM insertionrequired. Fill from exposure) beginning of the syringe.) Moisture ofbatch 0.3 g (vial) t = 0 Moisture (stability) Extra in vivo implantsover 25 will be used for moisture stability studies.

A more detailed summary of the stability sampling is provided in Table6. TABLE 6 Summary of Stability Samples. Number of Samples Temperature5° C. 40° C. Sam- Time point (months) ple 3 6 12 1 2 3 6 Par- 0.05 g0.05 g 0.05 g 0.05 g 0.05 g 0.05 g 0.05 g ticles 1 3 sys. 3 sys. 3 sys.3 sys. 3 sys. 3 sys. 3 sys. 2 3 4These additional systems were sampled for stability testing of omega-INFin suspension across all formulations. Stability test systems weresealed in glass vials under nitrogen. Stability testing for omega-INF ineach suspension formulation was performed at 1, 2, 3, and 6 months at40° C. and at 3, 6, and 12 months at 5° C. As a control, samples ofomega-INF particles were sealed in glass vials under nitrogen andassayed at 1, 2, 3 and 6 months at 40° C. and at 3, 6, and 12 months at5° C. stability samples were assayed for each time/temperature. Extrasamples were packaged and incorporated in the stability plan as moisturestudies. The stability of omega-INF in the suspension vehicle thatincludes benzyl benzoate and PVP is shown in FIG. 8.

The in vivo testing of each suspension formulation was conducted bysubcutaneously implanting the systems into Fischer rats. Twenty-threesystems were implanted unprimed while two systems were primed forapproximately seven days prior to implantation. After implantation(t=0), blood samples were drawn and omega-INF was assayed on day 5, 9,and 13 for each suspension formulation. Protein serum levels at days 5,9, and 13 after implantation are shown in FIG. 9. Protein serum levels 9days after implantation are shown in FIG. 10. FIG. 10 further includesprotein serum levels of samples described in Examples 3 and 4. As shownin FIG. 10, the serum levels of the omega-INF are within target ranges.Three systems were explanted at day 45 to assess system integrity. Theremaining systems were explanted at day 90, and all systems were intactindicating the implants performed in the planned manner. Twenty ratswere required to detect approximately 30% difference. Afterexplantation, systems/animals were tested for membrane expulsion, X-rayfor piston position (final explantation only), residual protein assay,macroscopic implantation site evaluation, clinical pathology (excisetissue and selected organs from all animals), implantation sitehistology at the DM, and assessment of capsule formation at thetitanium, polyurethane, and PEEK contacting areas.

Example 3 In Vivo and In Vitro Testing of Suspension Formulations Usinga Spiral Diffusion Moderator

The suspension formulations described in Example 2 were investigated forsystem integrity and in vivo release of omega-INF. This experimentdiffered from that described in Example 2 in that this experiment wasfocused on the ability of the suspension formulations to both releasemeasurable omega-INF in vivo as well as maintain system integrity usinga two-piece, spiral PEEK-on-PEEK diffusion moderator with a 0.25 mmdiameter and a 15 mm length. The suspension formulations were tested todetermine: omega-INF release in vivo from DUROS® systems after 2, 6, 9,and 13 days of in vivo operation (n=25); failure rates (systemintegrity) of in vivo systems at 29 days (n=3), 61 days (n=3), and 90days (n=19) after implantation; the stability of omega-IFN in thesuspension formulations over several months at 5° C. and 40° C.; and invitro release rate pumping into air and aqueous media. The materialsused in this experiment are shown in Table 7. TABLE 7 Materials Used inthe Studies. Omega-IFN Sucrose Methionine Citric Acid Monohydrate SodiumCitrate Povidone 17PF (cleaned) Lauryl Alcohol Benzyl Benzoate BenzylAlcohol DOPC Vitamin E DUROS ® Implants C-FLEX ® Piston FluoroelastomerPiston DUROS ® Osmotic Tablet Tecophilic HP-60D-33 DUROS ® MembraneTitanium Reservoir (Gen 3) with colored band Polyethylene Glycol 400Silicone Fluid, MDM 350 Spiral PEEK-on-PEEK DM (0.25 × 15 mm)

The suspension vehicles having the compositions shown in Table 8 wereprepared as described in Example 2. TABLE 8 Summary of SuspensionVehicle Composition (No omega-INF). Solvent Structuring Agent Com- Com-Nominal Ve- position position Viscosity hicle Solvent (% w/w) Agent (%w/w) Poise 1 Benzyl Alcohol 39 PVP 61 15,000 (BA) 2 Benzyl 49 51Benzoate (BB) 3 Lauryl Alcohol 45 55 (LA) 4 Vitamin E 52 DOPC 4810,000-60,000

The suspension formulations having the compositions shown in Table 9were prepared as described in Example 2. TABLE 9 Target Compositions ofSuspension Formulations. Vehicle Composition (90%) Drug ParticleComposition (10%) Content Content Sucrose Methionine Citrate ω-INFFormulation Solvent (% w/w) Agent (% w/w) (% w/w) (% w/w) (% w/w) (%w/w) PDP7-202-1 BA 35.1 PVP 54.9 3.3% 1.6% 3.5% 1.6% PDP7-202-2 BB 44.145.9 PDP7-202-3 LA 40.5 49.5 PDP7-202-4 Vit. E 46.8 DOPC 43.2

The systems were assembled and filled as described in Example 2, exceptthat spiral PEEK-on-PEEK diffusion moderators were used instead of thestraight PEEK diff-usion moderators of Example 2. Systems were built forin vivo, in vitro, and stability studies, with extra systems built toallow for characterization of the suspension formulation.Microbiological and humidity controls were implemented to minimizebioburden and water content in the product, as described in Table 7above. A representative number of systems were tested for bioburden andendotoxin to assess possible microbial contamination associated with thefinished implant product.

The systems were characterized as indicated in Table 10. A more detailedsummary of the stability-sampling plan is provided in Table 11. TABLE 10Characterization Testing of Final Systems. Tests Sampling quantity andformat per formulation In Vivo 27 Implants Protein Content Assay BB/PVP:24 implants (serve as stability BA/PVP, LA/PVP, VitE/DOPC: 15 implantssamples as well as homogeneity samples) Bioburden 3 Implants Endotoxin 1Implant X-ray All Viscosity 1 ml Density 2 ml (Extra suspension left insyringe) 10 systems (these systems also used for stability) Moisture ofbatch 5 implants Moisture (stability) Extra in vivo implants over 25used for monitoring the moisture of the stability samples over time. InVitro BB/PVP: 25 implants BA/PVP, LA/PVP, VitE/DOPC: 15 implants

TABLE 11 Summary of Stability Samples. Number of Implants at EachStorage Condition Temperature 5° C. 40° C. Time point (months) Sample 36 12 1 2 3 60 Particles 0.05 g 0.05 g 0 0.05 g 0 0.05 g 0 BA/PVP 3 3 0 30 3 0 BB/PVP 3 3 3 3 3 3 3 LA/PVP 3 3 0 3 0 3 0 VitE/DOPC 3 3 0 3 0 3 0

Implants used for stability testing were sealed in glass vials undernitrogen. The implants in this experiment contained different batches ofthe suspension formulations than those described in Example 2, so thestability of omega-INF in the current suspension batches was alsomonitored. If available, extra samples were packaged and incorporatedinto the stability plan to monitor changes in the moisture of thestability samples over time. As a control, samples of protein particleswere sealed in glass vials under nitrogen and assayed after 1 and 3months of storage at 40° C., and after 3 and 6 months of storage at 5°C. Three stability samples were assayed for each time and temperaturecombination.

The in vivo portion of this study was conducted by subcutaneouslyimplanting the systems into Fischer rats. In all groups, 25 systems wereimplanted. For the benzyl alcohol/PVP, benzyl benzoate/PVP, and laurylalcohol/PVP groups, 23 systems were unprimed and 2 systems were primed.For the Vitamin E/DOPC group, 15 systems were unprimed and 10 wereprimed. The PVP-based systems and the DOPC-based systems were primed forapproximately 7 and 5 days, respectively, prior to implantation.

Blood samples were drawn on days 2, 6, 9, and 13 after implantation andthe blood was assayed for omega-INF. Three systems were explanted on day29 and an additional three systems were explanted on day 61. Theremaining systems were explanted on day 90. After explantation,systems/animals were tested for: membrane and piston integrity; pistonposition (via X-ray); observations of diffusion moderator track andformulation in the drug reservoir; moisture content in the drugreservoir; residual protein content and characteristics (only in systemsexplanted at day 90); macroscopic implantation site evaluation; clinicalpathology (excised tissue and selected organs from all animals);implantation site histology at the diffusion moderator; and assessmentof capsule formation at the titanium, polyurethane, and PEEK contactingareas. Protein serum levels 9 days after implantation are shown in FIG.10. The serum levels of the omega-INF fell within the target ranges.

The in vitro portion of this study was conducted with approximatelytwo-thirds of the implants delivering the suspension formulation intoair and approximately one-third of the implants with the diffusionmoderators (DM) immersed in the appropriate aqueous buffer. Aqueousbuffers were selected based on a preliminary screening of release ratemedia performed by Analytical Sciences. Listed in Table 12 are the groupsize, diffusion moderator, and aqueous medium for each of the suspensionformulations. The membrane side of the implant was immersed in phosphatebuffered saline at neutral pH containing 0.2% sodium azide. The implantswith their diffusion moderators immersed in the aqueous medium wereunprimed so that both ends of the implant were hydrated on the same day.TABLE 12 Release Rate Experimental Plan. Diffusion Diffusion moderatorsmoderators exposed Aqueous exposed to aqueous medium on DM to air mediumside of implant BA/PVP (Spiral DM) 8 5 Phosphate buffer, pH 7 BB/PVP(Spiral DM) 10 5 Citrate buffer, BB/PVP (Straight DM) 10 0 pH 6 LA/PVP(Spiral DM) 10 5 Phosphate buffer, pH 7 VitE/DOPC (Spiral DM) 8 5Citrate buffer, pH 2The systems including the straight diffusion moderators and the benzylbenzoate/PVP suspension formulations were pumped to air only.

Example 4 Effect of Start-up Conditions and Diameter of the DiffusionModerator on In Vivo and In Vitro Performance

The effect of the start-up conditions (primed, unprimed) and diffusionmoderator diameter on the behavior of the systems were evaluated inthree suspension vehicles (BB/PVP, LA/PVP, and lauryl lactate (LL)/PVP).The experiment used a 2-piece, PEEK-on-PEEK, spiral diffusion moderatorwith a channel diameter of either 0.25 mm or 0.38 mm. The effect of thediffusion moderator diameter on omega-IFN serum levels and implantsurvival rates over a 90-day period was determined. The length of thediffusion moderator channel was 35 mm, which is longer than the 15 mmchannels used in the experiments described in Examples 2 and 3. Theinflux of water into the drug reservoir was monitored over time toanalyze the required length of the diff-usion moderator channel. Inaddition, the in vitro release of omega-IFN into buffer was studied.

Outputs of the in vivo portion of the study included determining serumlevels of omega-IFN on days 2 and 9, at two additional intermediatetimepoints, and approximately on days 75-90; failure rates (membraneintegrity) of in vivo systems at 13 days (n=2) and 90 days (n=7) afterimplantation; and water influx into the drug reservoir of the implant at13 days (n=2) and 90 days (n=7) after implantation. The groups used inthe in vivo portion of the study are shown in Table 13. TABLE 13Description of the Groups planned for the In Vivo portion of the Study.Description DM Inner DM Total Group Formulation Diameter Channel LengthPriming N/group 1 BB/PVP 0.25 mm 35 mm (2 piece) Yes 9 2 BB/PVP 0.25 mm35 mm (2 piece) No 9 3 BB/PVP 0.38 mm 35 mm (2 piece) Yes 9 4 BB/PVP0.38 mm 35 mm (2 piece) No 9 5 LA/PVP 0.25 mm 35 mm (2 piece) Yes 9 6LA/PVP 0.25 mm 35 mm (2 piece) No 9 7 LA/PVP 0.38 mm 35 mm (2 piece) Yes9 8 LA/PVP 0.38 mm 35 mm (2 piece) No 9 9 LL/PVP 0.25 mm 35 mm (2 piece)Yes 9 10 LL/PVP 0.25 mm 35 mm (2 piece) No 9 11 LL/PVP 0.38 mm 35 mm (2piece) Yes 9 12 LL/PVP 0.38 mm 35 mm (2 piece) No 9

The materials used in this experiment are shown in Table 14. TABLE 14Materials Used in the Studies. Drug Particles Omega-IFN SucroseMethionine Citric Acid Monohydrate Sodium Citrate Povidone 17PF(cleaned) Lauryl Alcohol (Spectrum Chemical) Benzyl Benzoate(Tessenderlo) Lauryl Lactate (Chemic Laboratories) DUROS ® ImplantsC-FLEX ® Piston Fluoroelastomer Piston Hydrosil Coating DUROS ® OsmoticTablet Tecophilic HP-60D-33 DUROS ® Membrane (clear) Titanium Reservoir(Gen 3) with colored band Polyethylene Glycol 400 Silicone Fluid, MDM350 Spiral PEEK-on-PEEK DM (0.25 × 35 mm) Spiral PEEK-on-PEEK DM (0.38 ×35 mm) Spiral PEEK-on-PEEK DM (0.25 × 15 mm)

The formulations of the omega-INF suspended in various vehicles weretested for stability, in vivo release, and in vitro release. Theomega-INF was prepared as described in Example 2. This study used 150microliter Gen 3 titanium reservoirs with color band fitted with clearTecophilic HP-60D-33 membranes annealed for 7 days at 65° C. in a lowhumidity forced air oven. Three suspension vehicles were prepared andtested: benzyl benzoate/PVP, lauryl alcohol/PVP, and lauryl lactate/PVP.A summary of the suspension vehicle compositions is presented in Table15. TABLE 15 Suspension Vehicle Compositions. Solvent Viscosity EnhancerComposition Composition Vehicle Solvent (% w/w) Agent (% w/w) 1 BenzylBenzoate 49 PVP 51 2 Lauryl Alcohol 45 55 3 Lauryl Lactate 50 50The suspension vehicles were prepared in 60 g lots. To minimize residualmoisture levels in the polymeric based formulations, lyophilized PVP wasused. The methionine and moisture content were measured in thelyophilized PVP before preparing the suspension vehicles. The suspensionvehicles were prepared using the Lightnin Overhead Mixer fitted with aspatula blade for the stirring paddle and then visually inspected forparticulates before proceeding. If necessary, the suspension vehicle wascentrifuged at 4000 rpm at 65° C. for 1 hour to remove any particles.The viscosity of the suspension vehicles was measured.

Target compositions of the suspension formulations are shown in Table16. TABLE 16 Target Compositions of Suspension Formulations. VehicleComposition (90%) Drug Particle Composition (10%) Content ContentSucrose Methionine Citrate ω-INF Formulation Solvent (% w/w) Agent (%w/w) (% w/w) (% w/w) (% w/w) (% w/w) PDP7-203-1 BB 44.1 PVP 45.9 3.3%1.6% 3.5% 1.6% PDP7-203-2 LA 40.5 49.5 PDP7-203-3 LL 45.0 45.0Each suspension formulation had a target particle loading ofapproximately 10% (w/w). The omega-INF was incorporated into thesuspension vehicle by hand using a metal spatula with the suspensionvehicle warmed on a hotplate. The suspension formulations were filled in10 mL syringes, deaerated under vacuum, and sealed in polyfoil pouches.The syringes were stored at room temperature in a dry box until fillinginto subassemblies.

The subassemblies and diffusion moderators were prepared as described inExample 3. To insert the diff-usion moderators for the LL/PVP suspensionformulations, the systems were placed into labeled vials membrane sidedown and stoppered but not crimped. The systems were removed from thedry box and fitted with spiral PEEK-on-PEEK diff-usion moderators withchannel dimensions of either 0.25 mm×35 mm or 0.38 mm×35 mm. The vialswere opened just prior to insertion of the diffusion moderators. Thevials were then restoppered and brought back into the dry box in batchesto ensure that the exposure time outside the dry box did not exceed 30minutes. Each system was equilibrated 30 minutes in the drybox inunstoppered vials before being restoppered and crimped.

To insert the diffusion moderators for the BB/PVP and LA/PVP suspensionformulations, the filled systems were placed back into the subassemblytrays. After the lid was put back in place, the subassembly trays weresealed in two layers of polyfoil bags and left in the dry box untilshortly before use. Packages of the subassembly trays were opened undernitrogen atmosphere inside of the isolator. Trays containing DM/DM guideassemblies were placed in tray heaters and allowed to equilibrate for atleast 30 minutes prior to insertion. Diff-usion moderators with 0.25 mmdiameter channels were heated to 75° C. Diffusion moderators with 0.38mm diameter channels were heated to 65° C. Each filled subassembly wascleaned on the outside with a sterile wipe, if needed, and seated in theDM insertion nest. After the nest was pressurized, a DM guide assemblywas placed over the end of the subassembly and the DM inserter wasimmediately activated. Diffusion moderator insertion was carried out atapproximately 3 mm/minute. After DM insertion, the system was allowed tosit in the nest for approximately 15 seconds and the end of the systemwas wiped with a sterile wipe. Systems were transferred from the nest tovials. After finishing a rack of 24 vials, vials were stoppered andcrimp sealed in the isolator.

The final systems were characterized as indicated in Table 27. TABLE 17Characterization Testing of Final Systems. Tests Sampling quantity andformat per formulation In Vivo 40 Implants Protein Stability BB/PVP: 9implants (also served as LA/PVP: 21 implants homogeneity samples)LL/PVP: 21 implants Bioburden 3 Implants Endotoxin 1 Implant X-ray AllN-Ray 24 implants (in vitro systems) Viscosity 1 ml (If extra suspensionremains in the syringes) Density 2 ml (If extra suspension remains inthe syringes) Moisture of batch at 4 implants t = 0 Moisture Extrasystems will be used for monitoring the moisture of the implants overtime. In Vitro BB/PVP: 24 implants LA/PVP: 30 implants LL/PVP: 24implants

A more detailed summary of the stability-sampling plan is given in Table18. TABLE 18 Summary of Stability Samples. Number of Implants at EachStorage Condition (in addition to t = 0) Temperature 5° C. 40° C.Timepoint (months) Sample 3 6 12 1 2 3 6 Particles 0 0 0 0.05 g 0 0.05 g0 BB/PVP 0 0 0 3 0 3 0 LA/PVP 0 3 3 3 3 3 3 LL/PVP 0 3 3 3 3 3 3

Implants used for stability testing were sealed in glass vials undernitrogen. The stability of the omega-INF in the BB/PVP suspensionvehicle was tested in previous experiments; therefore, a smallerstability schedule was tested in the current experiment. A largerstability study was conducted for the LA/PVP and the LL/PVP suspensionformulations since new sources of solvents were used in the presentstudy. If available, extra samples were packaged and incorporated intothe stability plan to monitor changes in the moisture of the stabilitysamples over time. As a control, samples of protein particles weresealed in glass vials under nitrogen and assayed at t =0 and after 1 and3 months of storage at 40° C. Three stability samples were assayed foreach time and temperature combination planned.

The in vivo portion of this study was conducted by subcutaneouslyimplanting the systems into Fischer rats. In each of the 12 groupsoutlined in Table 19, nine systems were implanted. In the groups thatwere primed, the length of priming was 4-5 days. TABLE 19 Description ofthe Groups Planned for the In Vivo portion of the Study. Description DMInner DM Total Group Formulation Diameter Channel Length Priming N/group1 BB/PVP 0.25 mm 35 mm (2 piece) Yes 9 2 BB/PVP 0.25 mm 35 mm (2 piece)No 9 3 BB/PVP 0.38 mm 35 mm (2 piece) Yes 9 4 BB/PVP 0.38 mm 35 mm (2piece) No 9 5 LA/PVP 0.25 mm 35 mm (2 piece) Yes 9 6 LA/PVP 0.25 mm 35mm (2 piece) No 9 7 LA/PVP 0.38 mm 35 mm (2 piece) Yes 9 8 LA/PVP 0.38mm 35 mm (2 piece) No 9 9 LL/PVP 0.25 mm 35 mm (2 piece) Yes 9 10 LL/PVP0.25 mm 35 mm (2 piece) No 9 11 LL/PVP 0.38 mm 35 mm (2 piece) Yes 9 12LL/PVP 0.38 mm 35 mm (2 piece) No 9

Blood samples were drawn on days 2 and 9 after implantation, and theblood was or omega-INF. Two systems were explanted on day 13 and theremaining systems were at day 90. After explantation, systems/animalswere tested for membrane and piston X-ray for piston position,observations of DM track and formulation in the drug reservoir, moisturecontent in the drug reservoir, residual protein content andcharacteristics (only in systems explanted at day 90), macroscopicimplantation site evaluation, clinical pathology (excise tissue andselected organs from all animals), implantation site histology at theDM, and assessment of capsule formation at the titanium, polyurethane,and PEEK contacting areas. Protein serum levels that were measured 9days after implantation are shown in FIG. 10. The serum levels of theomega-INF fell within the target ranges.

In the in vitro portion of this experiment, half of the implants wereprimed and the remaining half of the implants had the diffusionmoderator and membrane immersed in aqueous buffer on the same day(unprimed). The release rate medium was determined to be an appropriateaqueous buffer. Listed in Table 20 are the group size, diffusionmoderator, and start-up conditions for each of the suspensionformulations. TABLE 20 Description of Groups Planned for the In Vitroportion of the Study. Description DM For- Inner DM Start-up Total Groupmulation Diameter Channel Length conditions N/group 1 BB/PVP 0.25 mm 35mm (2 piece) Primed 6 2 BB/PVP 0.25 mm 35 mm (2 piece) Unprimed 6 3BB/PVP 0.38 mm 35 mm (2 piece) Primed 6 4 BB/PVP 0.38 mm 35 mm (2 piece)Unprimed 6 5 LA/PVP 0.25 mm 35 mm (2 piece) Primed 6 6 LA/PVP 0.25 mm 35mm (2 piece) Unprimed 6 7 LA/PVP 0.38 mm 35 mm (2 piece) Primed 6 8LA/PVP 0.38 mm 35 mm (2 piece) Unprimed 6 9 LL/PVP 0.25 mm 35 mm (2piece) Primed 6 10 LL/PVP 0.25 mm 35 mm (2 piece) Unprimed 6 11 LL/PVP0.38 mm 35 mm (2 piece) Primed 6 12 LL/PVP 0.38 mm 35 mm (2 piece)Unprimed 6 13 LA/PVP 0.25 mm 15 mm (2 piece) Primed 6The membrane side of the implant was immersed in phosphate bufferedsaline at neutral pH containing 0.2% sodium azide. Group 13 was includedas a control group.

The 72 systems in groups I through 12 were sent for N-ray imaging priorto testing in vitro to provide a greater level of detail about thesystems than can be provided by X-ray due to the superior resolution ofthe contents of the implant when N-ray is performed.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A nonaqueous, single-phase vehicle capable of suspending an activeagent, the nonaqueous, single-phase vehicle comprising at least onesolvent and at least one polymer, wherein the nonaqueous, single-phasevehicle exhibits phase separation upon contact with an aqueousenvironment.
 2. The nonaqueous, single-phase vehicle of claim 1, whereinthe at least one solvent is immiscible with water and wherein the atleast one polymer is soluble in the at least one solvent at aconcentration of greater than approximately 30%.
 3. The nonaqueous,single-phase vehicle of claim 1, wherein the at least one solvent isselected from the group consisting of benzyl benzoate, decanol, ethylhexyl lactate, and long chain (C8 to C24) aliphatic alcohols, esters,and mixtures thereof.
 4. The nonaqueous, single-phase vehicle of claim1, wherein the nonaqueous, single-phase vehicle exhibits phaseseparation upon contact with an aqueous environment having less thanapproximately 10% water.
 5. The nonaqueous, single-phase vehicle ofclaim 1, wherein the at least one polymer is selected from the groupconsisting of a polyester, pyrrolidone, ester of an unsaturated alcohol,ether of an unsaturated alcohol, polyoxyethylenepolyoxypropylene blockcopolymer, and mixtures thereof.
 6. The nonaqueous, single-phase vehicleof claim 1, wherein the at least one solvent comprises benzyl benzoateand the at least one polymer comprises polyvinylpyrrolidone.
 7. Thenonaqueous, single-phase vehicle of claim 1, wherein the nonaqueous,single-phase vehicle comprises from approximately 40% (w/w) toapproximately 60% (w/w) of the at least one solvent and fromapproximately 10% (w/w) to approximately 90% (w/w) of the at least onepolymer.
 8. A stable, nonaqueous suspension formulation, comprising: anactive agent and a nonaqueous, single-phase vehicle, the nonaqueous,single-phase vehicle comprising at least one polymer and at least onesolvent, wherein the nonaqueous, single-phase vehicle exhibits phaseseparation upon contact with an aqueous environment.
 9. The stable,nonaqueous suspension formulation of claim 8, wherein the at least onesolvent is immiscible with water and wherein the at least one polymer issoluble in the at least one solvent at a concentration of greater thanapproximately 30%.
 10. The stable, nonaqueous suspension formulation ofclaim 8, wherein the active agent is selected from the group consistingof baclofen, glial-cell line-derived neurotrophic factor, a neurotrophicfactor, conatonkin G, Ziconotide, clonidine, axokine, an antisenseoligonucleotide, adrenocorticotropic hormone, angiotensin I, angiotensinII, atrial natriuretic peptide, B-natriuretic peptide, bombesin,bradykinin, calcitonin, cerebellin, dynorphin N, alpha endorphin, betaendorphin, endothelin, enkephalin, epidermal growth factor, fertirelin,follicular gonadotropin releasing peptide, galanin, glucagon,glucagon-like peptide-1, gonadorelin, gonadotropin, goserelin, growthhormone releasing peptide, histrelin, human growth hormone, insulin, aninterferon, leuprolide, luteinizing hormone-releasing hormone, motilin,nafarerlin, neurotensin, oxytocin, relaxin, somatostatin, substance P,tumor necrosis factor, triptorelin, vasopressin, growth hormone, nervegrowth factor, a blood clotting factor, and a ribozyme.
 11. The stable,nonaqueous suspension formulation of claim 8, wherein the at least onesolvent is selected from the group consisting of benzyl benzoate,decanol, ethyl hexyl lactate, and long chain (C8 to C24) aliphaticalcohols, esters, and mixtures thereof.
 12. The stable, nonaqueoussuspension formulation of claim 1 1, wherein the nonaqueous,single-phase vehicle exhibits phase separation upon contact with anaqueous environment having less than approximately 10% water.
 13. Thestable, nonaqueous suspension formulation of claim 8, wherein the atleast one polymer is selected from the group consisting of a polyester,a pyrrolidone, an ester of an unsaturated alcohol, an ether of anunsaturated alcohol, a polyoxyethylenepolyoxypropylene block copolymer,and mixtures thereof.
 14. The stable, nonaqueous suspension formulationof claim 8, wherein the at least one solvent comprises benzyl benzoate,the at least one polymer comprises polyvinylpyrrolidone, and the activeagent comprises omega-interferon.
 15. The stable, nonaqueous suspensionformulation of claim 8, wherein the nonaqueous, single-phase vehiclecomprises from approximately 40% (w/w) to approximately 60% (w/w) of theat least one solvent and from approximately 10% (w/w) to approximately90% (w/w) of the at least one polymer.
 16. The stable, nonaqueoussuspension formulation of claim 8, wherein the active agent is presentin the stable, nonaqueous suspension formulation in an amount rangingfrom approximately 0.1% (w/w) to approximately 50% (w/w).
 17. Thestable, nonaqueous suspension formulation of claim 8, wherein theparticle containing the active agent is present in the stable,nonaqueous suspension formulation in an amount of approximately 3-12%(w/w).
 18. A method of preparing a stable, nonaqueous suspensionformulation comprising: providing a nonaqueous, single-phase vehiclecomprising at least one polymer and at least one solvent, wherein thenonaqueous, single-phase vehicle exhibits phase separation upon contactwith an aqueous environment; providing an active agent, wherein theactive agent is substantially insoluble in the nonaqueous, single-phasevehicle; and mixing the active agent and the nonaqueous, single-phasevehicle to form a stable, nonaqueous suspension formulation.
 19. Themethod of claim 18, wherein providing a nonaqueous, single-phase vehiclecomprising at least one polymer and at least one solvent comprisesselecting the at least one solvent to be immiscible with water andselecting the at least one polymer to be soluble in the at least onesolvent at a concentration of greater than approximately 30%.
 20. Themethod of claim 18, wherein providing a nonaqueous, single-phase vehiclecomprising at least one polymer and at least one solvent comprises usingat least one solvent selected from the group consisting of benzylbenzoate, decanol, ethyl hexyl lactate, and mixtures thereof.
 21. Themethod of claim 18, wherein providing a nonaqueous, single-phase vehiclecomprising at least one polymer and at least one solvent comprises usingat least one polymer selected from the group consisting of a polyester,a pyrrolidone, an ester of an unsaturated alcohol, an ether of anunsaturated alcohol, a polyoxyethylenepolyoxypropylene block copolymer,and mixtures thereof.
 22. The method of claim 18, wherein providing anonaqueous, single-phase vehicle comprising at least one polymer and atleast one solvent comprises using benzyl benzoate as the at least onesolvent and polyvinylpyrrolidone as the at least one polymer.
 23. Themethod of claim 18, wherein providing an active agent comprisesproviding an active agent selected from the group consisting ofbaclofen, glial-cell line-derived neurotrophic factor, a neurotrophicfactor, conatonkin G, Ziconotide, clonidine, axokine, an antisenseoligonucleotide, adrenocorticotropic hormone, angiotensin I, angiotensinII, atrial natriuretic peptide, B-natriuretic peptide, bombesin,bradykinin, calcitonin, cerebellin, dynorphin N, alpha endorphin, betaendorphin, endothelin, enkephalin, epidermal growth factor, fertirelin,follicular gonadotropin releasing peptide, galanin, glucagon,glucagon-like peptide-1, gonadorelin, gonadotropin, goserelin, growthhormone releasing peptide, histrelin, human growth hormone, insulin, aninterferon, leuprolide, luteinizing hormone-releasing hormone, motilin,nafarerlin, neurotensin, oxytocin, relaxin, somatostatin, substance P,tumor necrosis factor, triptorelin, vasopressin, growth hormone, nervegrowth factor, a blood clotting factor, and a ribozyme.
 24. The methodof claim 18, wherein providing an active agent comprises usingomega-interferon as the active agent.
 25. The method of claim 18,wherein providing a nonaqueous, single-phase vehicle comprises providinga nonaqueous, single-phase vehicle that exhibits phase separation uponcontact with an aqueous environment having less than approximately 10%water.